Fix gxyrs test failures caused by a Perl warning

Index: utils/gxyrs/gxyrs.pm
--- utils/gxyrs/gxyrs.pm.orig
+++ utils/gxyrs/gxyrs.pm
@@ -417,7 +417,7 @@ sub add_number_to_col {
 	}
 	
 	# Change offset to line's units.
-	if (! $units =~ /^$/) {
+	if ($units !~ /^$/) {
 	    $changed = change_text_units($units, $offset);
 	}
 	else {
